1. Field of the Invention
This invention is related to apparatus for detecting and indicating a tip-to-ground short in a subscriber line interface circuit (SLIC).
2. Description of the Prior Art
Subscriber line interface circuits which couple a two-wire communication path with a four-wire communication path are known, e.g., as disclosed in U.S. Pat. No. 4,041,252 (Earl T. Cowden) and copending U.S. application Ser. No. 564,637, filed Dec. 22, 1983. A known variation of these circuits has the feature that if the ring lead is connected to ground potential, the switch hook detection (SHD) output will be activated thus indicating an off-hook condition. The persistence of this condition, even after the line is serviced, is a sign of a fault condition. Thus the SLIC detects the ring-to-ground condition. However, a tip-to-ground condition does not trip the SHD output and thus remains undetected. It would be desirable to have a SLIC that can also detect a tip-to-ground condition and indicate it via the SHD output. This invention is intended to provide such a tip-to-ground detection and indication capability.